The present invention relates to a new and improved method of, and apparatus for, producing and selectively equalizing a temporal relationship between different signal sequences of digital signals.
Digital signal processing stages frequently cause time delays of the signals since such processing stages operate with the inclusion of delay members or units. When, for example, a digital audio signal is read-out from a record carrier, mixed with a further signal in a mixer unit or is otherwise modified, and then is recorded again on the record carrier, the newly recorded signal is temporally offset or shifted relative to the original record. The reason therefor is the conversion of the digital audio signal into an analog signal and vice versa during the use of an analog mixer unit. When a digitally operating mixer unit is used, the reason for the time delay is not the aforementioned conversion but the digital signal processing which is performed in the mixer unit as such.
Heretofore, the temporal or phase alignment of analog audio signals has been intended to be achieved in known manner by using a time code. For this purpose appropriate time code data are recorded on a related independent track of the record carrier. In this manner a number of audio signals can be aligned or placed in phase relative to each other by means of such time code.
Imperfect alignment of two associated audio signals which are recorded on different tracks of a record carrier and which are conjointly listened to, is perceived as an irritation. Such imperfect alignment may be attributed to the aforementioned delays during the digital signal processing. Furthermore, it must be considered that digital audio signals are recorded at a scanning or sampling frequency which is substantially greater than the frequency these two frequencies are not synchronized with respect to each other. One reason therefor is that frequently the scanning or sampling frequency and the time code frequency do not originate from the same clock signal generator. This circumstance has the further consequence that the time code cannot be used, during the processing of the digital audio signals, for the same control functions for which the time code is usually utilized during the processing of analog audio signals. For example, an editing operation can only be imprecisely performed on digital audio signals by means of the time code. Since, furthermore, the digital audio signal and the time code signal usually are not in synchronism, time delays between two parallelly appearing digital audio signals also cannot be indicated relative to a common time code.